At present sewing technology is quite mature. Many fast speed and simple sewing machines have been developed and mass production of high quality clothes and garments at lower costs is possible to benefit people. The earlier sewing machines that employ one needle and one thread and foot driving operation have been mostly replaced by automatic operation in the plant to enhance production efficiency and reduce cost.
As industrial sewing machines are required to achieve high production efficiency, to speed up stitching operation and reduce needle breaking is necessary. Nowadays sewing machines all adopt high speed motors to speed up stitching operation. However the needle tends to wobble in the high speed motion. In the condition of the needle being lowered at high speed and needle wobbling occurs, the probability of needle breaking increases. As a result, stitching operation is often interrupted. It becomes difficult to boost production efficiency.
Refer to FIG. 1 for a needle guard mechanism in a conventional sewing machine. It includes a front needle guard 13a connecting to a lower needle hook 40. When the axle 41 which controls the lower needle hook 41 rotates, the needle (not shown in the drawing) is moved downwards. When the needle is to be lifted upwards, the lower needle hook 40 starts operation to thread a looping yarn (not shown in the drawing), and moves the front needle guard 13a close to the rear needle guard 12a. The rear needle guard 12a is connected to the cloth driving teeth 42 which is driven by a connection beam 43. Therefore the rear needle guard 12a is pushed close to the front needle guard 13a to slightly clamp the needle. As the needle guard mechanism clamps the needle when the needle starts lifting, and the front and rear needle guards 13a and 12a are driven differently by the axle 41 and the connection beam 43, it is difficult to achieve accurate timing. As a result, needle broken or needle skip often occurs.